Limbo
Limbo itself can take many forms. When a new portal is opened it starts as an empty black room that slowly expands for the time it is open. Time moves exponentially slower in Limbo and it will infect anyone inside with Limbo Radiation. Limbo has tens of thousands of expanding cells, holding monsters and criminals that had been trapped inside. The inhabitants become more irradiated and hostile the longer they are inside. Limbo is controlled by Percival Higgsbury and is home to The Great Green One. Limbo can also take the form of a black goo and causes hallucinatory effects. A while ago in a place semi distant, there was this kingdom, right? This kingdom had a strange climate; where 3 months of the year crops would grow in an overabundance and the other 9 months froze the land over. The Old King put out a reward for anyone who could find a way to store the food for 9 months without it spoiling. This college of wizards were like “Shit, we could use the cash.” So the best students and their headmaster, the mysterious Great Green One, create a parallel dimension called limbo where time moves slower. The food could be left in Limbo for 9 months and only age around 3 days. The king loved it, but had no intention of paying the wizards. He sent his knights to kill off the wizards and their college. The Great Green One (Who may be shrek or luigi or the hulk, we don't know yet) disappeared into Limbo to hide. The king immediately began throwing food into Limbo for storage. The Great Green One began tampering with Limbo from the inside. He made the dimension unstable, so that whatever stayed in it for a extended period of time would suffer strange mutations. When the kingdom retrieved the food and began eating it, many became sick and died, while many more were mutated horribly. They formed a mob to go after the king, who fled into Limbo to hide. The Great Green One, Made one more adjustment. Instead of Limbo slowing time, it accelerated it greatly. The kings portal to Limbo was discovered and destroyed and he was lost in Limbo forever, his body being slowly corrupted until it was nothing but a tortured spirit. Years passed and Limbo was all but forgotten. Until some fuckin weak ass hero decided that instead of killing a dragon, he could trap it in Limbo for the reward. He dug up the ancient texts and opened a Limbo Portal to trap the beast. The success of Limbo as a means to capture any creature too powerful to kill spread. Eventually the practice became so common that Limbo was used as a prison. Over the years the abuse of Limbo started to have adverse effects on the environment. Once closed portals began to creak open, releasing Limbo radiation and mutating the life around it. A great lich stepped forward and took it upon himself to become the filter for Limbo. He tightly closed all Limbo portals and opened one inside of himself. Using spells n shit he was able to keep the radiation under control. He lived in isolation until eventually the radiation overtook him. When he died, no volunteer could be found to take his place. Without a better idea, a random prisoner was chosen to take the Liches soul and become the filter for Limbo. They bound the Phylactery to an isolated forest called the Talwarie woods. Every few hundred years a new sacrifice was given the task of becoming the Limbo filter.